Upon the fabrication of a semiconductor, a semiconductor device is formed by a lithography technique in which a resist is applied onto the surface of a silicon wafer to form a photosensitive film, the film is exposed to light so as to form a latent image and the latent image is then developed to form a negative or positive image. A negative resist composed of cyclized polyisoprene and a bisdiazide compound has heretofore been known as a resist composition for the fabrication of semiconductor devices. However, the negative resist involves a drawback that it cannot be accommodated to the fabrication of semiconductors integrated to high degrees because it is developed with an organic solvent, so that it swells to a significant extent and its resolving power is hence limited.
With the fabrication of highly integrated semiconductors, on the other hand, positive resists, which are developed with an alkali and composed of an alkali-soluble novolak resin and a quinonediazide compound, have come to be widely used because they do not swell and are excellent in resolving power in themselves. It is also possible to form minute patterns of 1 .mu.m or smaller in line width owing to the enhancement of resolution by the improved performance of positive resists and the development of a high-performance aligner.
Incidentally, it is necessary to more rigidly control the dimensions of a resist in the formation of a minute pattern of 1 .mu.m or smaller, particularly 0.8 .mu.m or smaller in line width. However, satisfactory results as to such a requirement are not necessarily obtained from the conventional positive resist compositions. There has been a strong demand for the development of a positive resist composition good in dimensional controllability.